Method of applying a wax composition to the convex countersink portion of a can end



QRTLEITT 2,906,640

METHOD OF APPLY A W COMPOSITION TO THE CONVEX COUNTE NK PORTION OF A CAN END Filed May 1, 1956 Sept. 29, 1959 9 COMPLETELY FLUID HYDROCARBON WAX COMPOSITION UNDER PRESSURE v EJ ECTED COMPOSITION AT INCREASED VISCOS|TY SEMI'SOLID GEL COMPOSITION "IIIIII'II V'IIIIIIIII/ HYDROCARBON WA COMPOSITION COUNTERSINK RADIUS V IN VEN TOR. RAY/14mm M.B19R7ZTT A TTMQNFKS Staes Unite METHOD OF APPLYING, A' COMPOSITION TO CONVEX COUNTERSINK- PORTION OF A CAN END- Raymond ML Bartlett, Floral" Park, N.Y;, assignorto American-- Can Company, New York,-N.Y., a corporation ofNew Jersey Application May 1, 1956, Serial No. 581,950

2 Claims. (Cl; 117-43) The present invention pertains to amethod of applying a coating, composition to an article. and more specifically it pertains to a method of applying-a wax composition to, aparticular portion of a metallcan end.-

In the canning. of'rcertain products, e.g carbonated softdrinks, it was observed thatscorrosiontof the countersink radius of the metal canendoccurred. It'is this part of the end-which is subjected tothe greatest strain,

in the drawing; and stamping; of the'end-frornflatmetal sheets. This corrosion was sometimes suflicientlysevere Although the means for preventing corrosion to the. countersinkradiusof-the can end was known, there was,

presented the problem of applying-the wax-rubber com-: position to this restricted portion of the can end, efii ciently and-at a high rate of speed.

Numerous attempts to spray, roll or iron on, the coating =material" as a-- hot melt, iae. solvent-free and molten, composition met with failure. Inall ofthese ex+.

periments, the coatingcompositionwouldeither solidify too rapidly upon contacting the can wherebva lumpy, discontinuous and insuflicient coating would result; or the coatingwould be too fluid uponcontaeting; .the can end whereby-it-would be displaced fromttheend upon rapid movement or revolution-thereof, or flow to undesired portions of the can endi It is therefore an object of the present invention to-providea method whereby the'protective coatingof a waxrubber composition may be applied efliciently andat high speed to a restricted portion of the can end.

A further object of the inventionis PIQVide a method of thecharacter-described wherein the coating composition can-be madeto flow outover a predeter mined; restricted area of a metalcan end moving or re-. volving at. a high rate ofspeed.

Numerousother objects and advantages of theillventionwill be-apparent ash is better understood fromthe following description, which, taken -in connection with the accompanying drawings, discloses apreferredembodiment thereof.

I have discovered that the aforementioned and other objects can beaccomplished by providing a'wax-rubber composition-dissolved and dispersed in a volatile hydrocarbon solvent, maintaining'the resultantsuspensionat; an elevated temperature and pressure, forcibly ejecting the suspension from a suitable orifice in a fine-stream and causing it to'impinge-upou the countersink radius of the from the orifice and its point of impingement on the can end andsimultaneously evaporating some of the solvent from said suspension whereby, due to the combined effectsof the coolingand solvent evaporation, the suspension tent increases; in viscosity to a paste or grease-like gel between the -tin 1eit is ejected from the orifice and the time it flows-out on the can end, causing said increased viscosity suspension tofiow out or spread radially from the point of impingement'of the fine stream due to the force of the impingement. on the can end to form a continuous film over the predetermined portion of the can end, and thereafter leveling the filmand' evaporating the residual solvent from the suspension to cause said wax-rubber composition to. set to a substantially rigid solid.

Referring to the drawings:

Fig. l is' a schematic sectional View in perspective with parts broken away showing the application of a waxrubber composition to the countersink radius of a can end-in inverted position; and

Fig. 2'is aperspective sectional view f' a can end in inverted positionwith parts broken away showing the disposition of; the wax-rubber composition after completion; of thesteps' of the present invention.

The-success of the method-of the instant invention depends upon the ability of the coating material to go through. aphase-ofsemiorpseudo solidit-y or gel phase between-its completely fluid audits solid phases. In otherlwords, the completelyfluid coating composition, by the cooling thereof and by the partial evaporation of solvent therefrorn, changes first into a grease-like or pastelike gel, and thereafter becomes a substantially rigid solid: after complete solvent removal and cooling to room temperature. By careful control of the conditions of temperature, pressure and the composition of the coat ingmateriahl have been able to-bring about the change in the composition from complete fluidity to semi-solidity or a;grease likeconsistency-in a very brief period of time,- Afterassuming-this grease-like consistency, the composition is sufiiciently deformable to flow out and cover thedesired portion of the can end under the influeHQt of" certain forces, and-yet has reached a point of sutficient rigidity-whereby'it Willnot splash appreciably, flowindiscriminately-over undesired portions of the object to be coated or bedislodged from the article moving at-high speed.

As a-preferred or exemplary embodiment of the instant invention thedrawings illustrate in Figure l the can end 10 ininverted 'position consisting of a central or countersunk panel 11 which merges into a' substantially vertical-surrounding ,wall'section 1 2, which-in turn merges into an annular substantially.horizontal-flange 13, which flange terminates in an inwardly curved or curled edge 14. The countersink radius 15 is the curved portion of the canend-extending between the countersunk panel 11 and the vertical wall section 12'.- By means of any suitable mechanism (not shown), can end 10 is being rotated at a relatively high-angular velocity in a direction indicated by the arrow.

From-a suitably aligned device such as the nozzle 16 illustrated-in Figure l, whichnozzle is shown spaced a distance'above-can end- 10, a coating composition comprising, by weight, parts of microcrystallinewax, 5 partsparaflin wax, 5 parts Butyl rubber, all dissolved and dispersed in hexane to give a composition having about 44% bytweight total solids, is ejected under pressure in a fine stream'17 toward and-onto the countersink radius 15. By any suitable apparatus (not shown) the nozzle 16 or other applicator means is maintained at a constant temperature so-that the coatingcomposition as it leaves the nozzle is at a temperature of about F. Also, from asuitable source (not shown), 3 to 5 pounds per square inch (p.-s.i.) gage pressure, inthe form of compressed air, is applied to the material to eject it forcibly from nozzle :16,

Due to the sudden release of pressure as the material emerges from the nozzle 16 and also due to the elevated temperature at which the coating is maintained, the hexane solvent begins to evaporate at a rapid rate, causing an increase in total solids and thereby an increase in viscosity of stream 17 as it travels toward the countersink radius 15. The viscosity of stream 17 is further increased by the cooling thereof due to the heat taken up by the evaporation of the solvent (latent heat of vaporization) and the air at room temperature surrounding the stream 17. Upon contact with the countersink radius 15, the viscosity of stream 17, has increased to a point where, instead of being completely fluid, i.e. having a Brookfield viscosity of less than 25 centipoises, as it was upon emergence from nozzle 16, it now gelled or assumed a pasteor grease-like consistency having a Brookfield viscosity in excess of 1,000 centipoises. Also by the combined cooling effects mentioned above and by contact with the cam end which is preferably maintained at room temperature, the composition composing stream 17 has cooled to a temperature of about 120 F. As the composition contacts the end, its percent total solids value has increased to about 54% due to the loss of solvent therefrom.

The force of impingement of the fine stream 17 onto the counter sink radius 15 under the influence of the pressure by which the stream is ejected from nozzle 16 causes the coating composition to flow or spread out radially from the point of impingement. As stated previously, by regulating the proportions of ingredients of the composition, the pressure and temperature conditions and thereby its viscosity as it strikes can end 10, the amount of radial flow-out of the composition on the can end can be regulated. In the preferred or exemplary embodiment illustrated, the centrifugal force exerted on the coating composition due to the rapid spinning of the end causes the composition to flow a greater extent radially outwardly from the center of the can end than towards the center of the can end. This greater radial outward flow is desired in order to have the coating cover that portion of wall section 12 which will be exposed to the product in the finished, packed can. It is believed that portions of the can end, such as wall section 12 and countersink radius 15, which have been subjected to bending and shaping operations during fabrication of the end, are more susceptible to corrosion due to disturbance of the base metal and/ or its protective coating, e.g. tin, organic enamel, etc., during these operations. However, the amount of flowout and the direction thereof can be varied to cover any desired area of any type of article by varying the controlling conditions enumerated above, i.e. temperature, pressure, and composition of the coating material, by varying the angle of impingement of stream 17, and/or movement of the article to be coated, e.g. slower or faster angular velocity to vary the centrifugal force exerted on the coating, straight line motion instead of rotational motion to obviate any centrifugal force.

After complete deposition of an annular ring of coating composition to the countersink radius 15, any residual solvent left in the coating is then removed as for example by passing the coated end into an oven and maintaining it at an elevated temperature for a suflicient time. During this time, the heat causes the surface of the coating to level and become smooth. When the drying, i.e. solvent removal and leveling operation are complete, the countersink radius 15 has a thin, continuous, smooth coating of 100% solids composition thereon extending laterally from countersink radius 15 a short distance onto the countersink panel 11 and down the vertical wall 12, as best seen in Fig. 2.

The proportions and types of ingredients specified in the preferred embodiment above may be varied within certain limits and still obtain satisfactory results. Microcrystalline waxes having a melting point between 150 F. and 205 F. and preferably about 170 F. may be used in an amount of from 90 to 97 parts by weight. High melting point waxes having similar properties may also be used, eg LG. waxes, montan waxes and ceresins. The

paraffin wax specified above is a hydrocarbon wax having a melting point of about 155 F. Other wax like materials having a melting point in the range of 130 F. to 170 F. and which are compatible with the other components of the composition, such as beeswax, vegetable wax, and certain resins, e.g. polyethylene, may also be used. The lower melting wax component of the composition is present in proportions of 0 to 5 parts by weight. Other rubbers, natural or synthetic, may be used in place of the Butyl rubber specified above, providing they are compatible with the wax used in the composition and they are soluble in the solvent used. Examples of such other rubbers are: natural rubbers such as pale crepe, balata and gutta-percha; and synthetic rubbers such as polybutadiene, polyisobutylene, styrenebutadiene elastomers, Pliolite (Goodyear product made by refluxing a benzene solution of the high-grade, low protein rubber with an amphoteric metal halide, such stannic chloride) and halogenated rubber. These rubber materials are present in proportions ranging from 3 to 10 parts by weight.

The solvent useful in the present invention is a hydrocarbon sovent, and preferably a 5 to 8 carbon atom alkane, having at atmospheric pressure a boiling range I tion are a function of the operating temperatures and the percent total solids of the composition. For the temof about from 80 F. to 250 F. Solvents with a boiling point above 250 F. are unsuitable in that they will not be sufficiently volatile at application temperatures to flash-off from the composition as it emerges from the I nozzle or other applicator orifice; while solvents having a boiling point below the minimum tend to generate too high a vapor pressure at the working temperatures.

The various viscosities obtaining in the present invenperatures of operable semi-solidity given hereinafter, i.e. 90 F. to 190 F. and preferably 120 F. to 160 F., the composition as it contacts the article to be coated contains about from 10% to and preferably 35% to 55% by weight total solids. The percent total solids of the composition prior to its ejection from the orifice will be somewhat lower than those given immediately above due to a greater proportion of solvent in the composition.

The action of the hydrocarbon solvent on the solids of the composition is more in the nature of a solventdispersing medium than a true solvent. It does have a solvating effect on the rubber component; but the wax component, in the amounts used in the present invention, is dispersed therein in a molten state. The principal function of the hydrocarbon solvent is to enable the composition to go from a completely fluid phase to a gel or grease-like phase upon cooling and partial solvent removal in a controllable, brief period of time, whereby the coating composition may be handled as a low viscosity liquid in the coating apparatus but functions on the article to be coated as a high viscosity gel.

As stated previously, viscosity of the coating composition will depend upon the make-up of the composition and its temperature. For compositions of the type useful in the present invention, the operable viscosity of the composition when it is completely fluid, i.e. before and up to its ejection from the orifice, is less than 50 and preferably less than 25 centipoises. After the composition assumes its grease-like consistency, i.e. after striking and flowing out on the article to be coated, it has a visloss of solvent.

The composition must be heated at least to a temperature at which it is completely fluid, i.e. has a Brookfield viscosity of less than 50 centipoises. This fluidization temperature will vary directly with the percent solids in the composition and the melting point of these solids, principally the high melting point wax. For a composition of the type described above, the fluidization temperature range is about from 100 F. to 200 F. and preferably 130 F. to 170 F. In order to avoid developing too high a vapor pressure of the solvent and consequent sputtering as the composition leaves the applicator orifice, and to obviate the necessity of a great amount of cooling of the composition after it leaves the orifice, the composition should not be heated above the boiling point of the solvent at atmospheric pressure.

Conversely, in the instant method, the composition must be cooled to a temperature below its fluidization temperature as it flows out on the article to be coated so that it has its desired high viscosity, i.e. 1,000 centipoises or more, and a gel or grease-like consistency. Since the change from complete fluidity to operable semi-solidity is relatively gradual, i.e. there is no sharp division between the two phases, the temperature at which the composition assumes its operable grease-like consistency will be at least about F. below the fluidization temperature. For the composition described hereinbefore, this temperature of operable semi-solidity is in the range of about from 90 F. to 190 F. and preferably 120 F. to 160 F. As long as the composition retains an appreciable amount of solvent, it will maintain its operable, semi-solid, greaselike consistency at temperatuers well below the freezing or solidification temperature of the composition containing little or no solvent, and even down to room temperature, i.e. 70 F.

The total pressure, in excess of atmospheric pressure, exerted on the completely fluid composition prior to its ejection from the nozzle or other applicator means is the sum of the vapor pressure produced by the heated solvent and pressure supplied from an external source, such as compressed air. This total pressure is above atmospheric pressure so that the composition is forcibly ejected from the applicator means to cause it to flow outwardly from the point of contact with the article to be coated and also so that solvent will flash-off from the composition upon emergence thereof into an atmosphere of reduced pressure. However, the total pressure must not be so high as to cause the composition to sputter or, in effect, he unrestrictedly sprayed or atomized as it emerges from the applicator orifice.

The total pressure may be varied by varying the type of solvent and the temperature thereof within the limits set forth above; and/ or by varying the pressure supplied from the external source. The preferred method of total pressure control is by varying the pressure supplied from the external source. The magnitude of the externally supplied pressure will depend upon a number of independent factors, e.g. the make-up of the coating composition, including the boiling point of the solvent, the temperature to which the composition is heated and the type of equipment used. Guided by the limitations and restrictions on the total pressure set forth above, the magnitude of the externally supplied pressure will be readily apparent to one skilled in the art. Preferably this pressure will be in the range of 1 to 10 p.s.i. gage.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the steps of the method described and their order of accomplishment without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the method hereinbefore described being merely a preferred embodiment thereof.

I claim:

1. A method of applying a wax composition to the convex countersink portion of an can end comprising, heating a mixture containing a hydrocarbon wax and a 6 to 8 carbon atom alkane to a temperature of about F. to 170 F. and not above the boiling point of the alkane to form a homogeneous liquid composition having a Brookfield viscosity of less than 50 centipoises, ejecting a non-atomized stream of said liquid composition toward said can end by means of superatmospheric pressure of 1 to 10 p.s.i.g. whereby a portion of said alkane evaporates from said stream, impinging said stream onto said countersink portion, simultaneously with said evaporation cooling said stream to a temperature at least 10 F. below the aforesaid heating temperature to solidify said hydrocarbon wax and enclose the unevaporated alkane remaining in said stream within said solidified wax whereby said stream upon contacting said article has a paste like consistency with a viscosity of at least 1,000 centipoises, and spreading and leveling said impinged stream over said area by at least the force of said impingement.

2. A method of applying Wax composition to the convex countersink portion of an can end comprising, heating a mixture containing by weight about 90 to 97 parts of a microcrystalline wax having a melting point between F. and 205 F., about 0 to 5 parts of a parafiin wax having a melting point between 130 F. and F., about 3 to 10 parts of an organic solvent soluble rubber, and a 6 to 8 carbon atom alkane to a temperature of about 130 F. to 170 F. and not above the boiling point of said alkane to form a homogeneous liquid composition having a Brookfield viscosity of less than 50 centipoises, ejecting a non-atomized stream of said liquid composition toward said can end by means of superatmospheric pressure of 1 to 10 p.s.i.g. whereby a portion of said alkane evaporates from said stream, impinging said stream onto said countersink portion, simultaneously with said evaporation cooling said stream to a temperature at least 10 F. below the aforesaid heating temperature to solidify said hydrocarbon wax and enclose the unevaporated alkane remaining in said stream within said solidified wax whereby said stream upon contacting said article has a paste like consistency with a viscosity of at least 1,000 centipoises, and spreading and leveling said impinged stream over said area by at least the force of said impingement.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,096 Bogin Mar. 7, 1939 2,342,643 Cessna Feb. 29, 1944 2,376,777 Kallander May 22, 1945 2,732,315 Birkland Jan. 24, 1956 2,754,228 Bede July 10, 1956 2,790,736 McLaughlin Apr. 30, 1957 FOREIGN PATENTS 525,373 Great Britain Aug. 27, 1940 

1. A METHOD OF APPLYING A WAX COMPOSITION TO THE CONVEX COUNTERSINK PORTION OF AN CAN END COMPRISING HEATING A MIXTURE CONTAINING A HYDROCARBON WAX AND A 6 TO 8 CARBON ATOM ALKANE TO A TEMPERATURE OF ABOUT 130*F. TO 170*F. AND ABOVE THE BOILING POINT OF THE ALKANE TO FORM A HOMOGENEOUS LIQUID COMPOSITION HAVING A BROOKFIELD VISCOSITY OF LESS THAN 50 CENTIPOSES, EJECTING A NON-ATOMIZEKD STREAM OF SAID LIQUID COMPOSITION TOWARD SAID CAN END BY MEANS OF SUPERATMOSPHERIC PRESSURE OF 1 TO 10 P.S.I.G. WHEREBY A PORTION OF SAID ALKANE EVAPORATES FROM SAID STREAM, IMPINGING SAID STREAM ONTO SAID COUNTERSINK PORTION, SIMULTANEOUSLY WITH SAID EVAPORATION COOLING SAID STREAM TO A TEMPERATURE AT LEAST 10*F. BELOW TH AFORESAID HEATING TEMPERATURE TO SOLIDIFY SAID HYDROCARBON WAX AND ENCLOSE THE UNEVAPORATED ALKANE REMAINING IN SAID STREAM WITHIN SAID SOLIDIFIED WAX WHEREBY SAID STREAM UPON CONTACTING SAID ARTICLE HAS A PASTE LIKE CONSISTENCY WITH A VISCOSITY OF AT LEAST 1,000 CENTIPOISES, AND SPREADING AND LEVELING SAID IMPINGLED STREAM OVER SAID AREA BY AT LEAST THE FORCE OF SAID IMPINGEMENT. 